package com.imooc.bigdata.hadoop.mr.wc;/**
 * Created by luochangyong on 2019/7/3.
 */

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

import java.io.IOException;
import java.util.Iterator;

/**
 *
 */
public class WordCountReducer extends Reducer<Text, IntWritable, Text, IntWritable> {
    /**
     * (hello, 1) (world, 1)
     * (hello, 1) (world, 1)
     * (hello, 1) (world, 1)
     * (welcome, 1)
     *
     * map的输出到reduce端，是按照相同的key分发到一个reduce上去执行
     *
     * reduce1:(hello, 1)(hello, 1)(hello, 1) ==> (hello, <1, 1, 1>)
     * reduce2:(world, 1)(world, 1)(world, 1) ==> (world, <1, 1, 1>)
     * reduce3:(welcome, 1) ==> (welcome, <1>)
     *
     * Reducer和Mapper中其实使用了模板模式
     */
    @Override
    protected void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
        int count = 0;
        Iterator<IntWritable> iterator = values.iterator();
        //<1, 1, 1>
        while(iterator.hasNext()){
            IntWritable value = iterator.next();
            count += value.get();
        }

        context.write(key, new IntWritable(count));
    }
}